Hydraulic brake fluid base oils

ABSTRACT

NOVEL HYDRAULIC BRAKE FLUIDS WHEREIN THE BASE OILS ARE AN ADDUCT OF A MIXTURE OF ETHYLENE OXIDE AND 1,2-PROPYLENE OXIDE WITH CASTOR OIL, AND ARE CHARACTERIZED BY HAVING GREATLY IMPROVED PROPERTIES, IN CONNECTION WITH THEIR USE IN BRAKE FLUIDS, OVER THE PROPERTIES OF CASTOR OIL ALONE OR IN COMBINATION WITH EITHER ETHYLENE OXIDE OR 1,2-PROPYLENE OXIDE.

United States Patent Int. Cl. C09k 3/00 US. Cl. 252-79 5 Claims ABSTRACT OF THE DISCLOSURE Novel hydraulic brake fluids wherein the base oils are an adduct of a mixture of ethylene oxide and 1,2-propylene oxide with castor oil, and are characterized by having greatly improved properties, in connection with their use in brake fluids, over the properties of castor oil alone or in combination with either ethylene oxide or 1,2-propylene oxide.

This invention relates to base oils for hydraulic brake fluids and to brake fluids produced therefrom. The base oils of this invention are an adduct of a mixture of ethylene oxide and 1,2-propylene oxide with castor oil, and are characterized by having greatly improved properties, in connection With their use in brake fluids, over the properties of castor oil alone or in combination with either ethylene oxide or 1,2-propylene oxide.

This application is a division of application Ser. No. 176,126, filed Feb. 27, 1962, and now abandoned, which is a continuation-in-part of application Ser. No. 690,417, filed Oct. 16, 1957, now abandoned, which is a continuation-in-part of application Ser. No. 629,585, filed Dec. 3, 1956, now abandoned.

Hydraulic brake fluids are often subjected to extreme temperature variations and must be so constituted that they retain a relatively invariable viscosity, a homogeneous mixture and resist decomposition, solidfication and separation of the ingredients throughout the temperature range to Which they are exposed. Castor oil has proven to be deficient in several respects as a base oil for hydraulic brake fluids. These deficiencies include relatively poor low temperature properties, inadequate water tolerance, and relatively low viscosity indexes. Presently available synthetic base oils of the polyalkylene glycol type provide brake fluids characterized by having insufficient lubricity.

An object of this invention is to overcome these and other undesirable characteristics by providing base oils for hydraulic brake fluids which are characterized by improved low temperature properties, improved viscosity indexes, improved Water tolerances, and improved lubricity, as well aslsurpassing the other established requirements for such base oils. Another object is to provide improved hydraulic brake fluids for heavy duty application containing the base oils of this invention. Other objects of this invention will be evident from the following specification.

In accordance with this invention it has been found that when mixtures of ethylene oxide and 1,2-propylene oxide are added to castor oil in predetermined proportions in a predetermined manner new and useful com- ICE positions are obtained which are characterized by stability at low temperatures. The products of this invention differ radically in their compositions from glycol and polyglycol esters of castor oil which have previously been suggested for use in hydraulic brake fluids. The products of this invention are for hydraulic use far superior to those glycol esters of castor oil, and as described below, exhibit excellent response to standard commercial tests: particularly as to complete or substantially complete lack of haze or opalescence after prolonged exposure to low temperatures.

The products of the invention are formed by sequentially reacting ethylene oxide with the castor oil and then reacting said mixture with the propylene oxide, or by simultaneously reacting ethylene oxide and 1,2-propylene oxide with the castor oil, either by simultaneously adding the oxides separately to the castor oil or mixing the oxides prior to reaction With the castor oil.

Satisfactory produucts for use as base oils in this invention are those which are miscible with a minimum of 10% of water at room temperature, and which, in the form of a 20% solution by weight in 2-butoxyethano1, are characterized by having the ability to flow within 5 seconds and by being free from appreciable hazing after being maintained at 40 F. for 6 days.

In general, the satisfactory best products of this invention include the finished adduct containing from about 25% to about 45% by weight of a total mixed oxide component comprising about 90% ethylene oxide and about 10% propylene oxide; the finished adduct containing from about 25% to about 55% by weight of a total mixed oxide component comprising about ethylene oxide and about 20% propylene oxide; the finished adduct containing from about 45% to 65% by weight of a total mixed oxide content comprising about 60% ethylene oxide to 40% propylene oxide. Satisfactory results are obtained when the reaction is carried out so that the products have com-positions Within the following limits:

Percent by weight Castor oil 35-70 Propylene oxide 2 /250 Ethylene oxide 5-50 For example, a product of particularly fine performance has a composition of 45% mixed oxides (60% ethylene, 40% propylene) and 55 castor oil.

Suitable diluents for use in the hydraulic brake fluids of this invention are organic oxygen-containing compounds selected from the group consisting of aliphatic monohydric, 'dihydric, and trihydric alcohols having from 1 to 7 carbon atoms and aliphatic ether alcohols having from 3 to 10 carbon atoms. Examples of diluents within this category include methyl alcohol, ethyl alcohol, propyl alcohols, butyl alcohols, amyl alcohols, diacetone alcohol, ethylene glycol, propylene glycol, mehyl pentanediol, and dipropylene glycol, hexylene glycol, glycerine, 2-rnethoxyethanol, 2-ethoxyethanol, Z-butoxyethanol, methoxy-methoxyethanol, and the mono-methyl, mono-ethyl, and mono-butyl ethers of diethylene glycol.

The base oils of this invention have been found to have good compatibility, even at low temperatures, with diluents of the type listed above. Excellent brake fluids can be prepared by the use of 20% by weight of a base oil of this invention and 80% by weight of one or more of the foregoing diluents. Of course, the relative amounts of base oil and diluent can be varied as desired, with a preferred (7) Slight precipitate on bottom amount of diluent being from about 60 to about 90 weight percent, based on the combined weight of the base oil and diluent.

The instant base oils have much lower viscosities at reduced temperatures than do the prior art unmodified esters. This fact results in an extension in the number of permissible diluents, including those with higher viscosities, over those which could previously be used. Some vis- (8) Heavy precipitate on bottom (9) Phase separation 10) Solid or gelled A passing rating in this test is from 1 to 3, with 3+ being on the borderline. It will be noted that hydraulic fluids containing the base oils of this invention (Examples 1-4, 6-12) pass this test without difliculty. The fluids containing base oils having too high a percentage of an oxide cosity data on the base oils of this invention, as well as 10 (Examples 5, 13), on the other hand, are not able to pass TABLE IL-GOLD TEST DATA Example number 1 2 3 Base oils:

Castor oil:

30% mixed adduct AL.-.

40% mixed adduct A-.. 50% mixed adduct A 30% mixed adduct BL- 40% mixed adduct B 50% mixed adduct B 2Q 20 60% mixed adduct B Diluents:

Celanese 901 H- n-Butanol 3-methyl butanol. Hexylene glycol Methyl isobutyl carbinol...

Cold test ratmgs 1 90% 021140, 10 CsHaO adduct.

on previously available ricinoleic acid esters, are presented in Table I.

TABLE I.VISCOSITY DATA Viscosity Kinematic index Pour viscosity, 0 F. (A.S.T.M. point, Base oil (centistokes) D56753) F.

Castor oil. Ca. 75, 000 84 10 Blown castor oil (visc.: 23 stokes at 25 C.) 95 0 Ethylene glycol mononieinoleate. Ca. 100,000 65 5 Propylene clycol monoricmoleate- Ca. 100, 000 36 -15 Castor oil, mixed adduct AL. Czmtor oil, mixed adduct AL. Ca. 12, 000 127 35 Castor oil, mixed adduet AL. -5 Castor oil, 30% mixed adduct 13 35 Castor oil, 40% mixed adduct BL. Ca 10 000 127 40 Castor oil, 50% mixed adduet BL. -45 Castor oil, 60% mixed adduct BL. -15

(11190? (321140, 10% CQHQO adduct. 80% CZHAO, 20% C H O In general, the higher the viscosity index, the lower is the change of viscosity with temperature. Thus, high viscosity indexes parallel low viscosities at reduced temperatures. It will be noted that the instant base oils have desirably higher viscosity indexes than do the previously available esters. A rough correlation also exists between pour points of base oils and the abilities of hydraulic brake fluids containing the oils to pass the necessary cold tests. In general, the dividing line between acceptable and non-acceptable base oils appears to be in the vicinity of a pour point of -20 F. Most of the instant base oils have pour points at or below this dividing line, while the previously available esters do not. Some of the oxide adducts containing higher percentages of alkylene oxide have high pour points, and, as revealed by Table II, brake fluids containing these adducts fail to pass the cold test.

In Table II, data are presented on the results of cold tests run on hydraulic brake fluids containing base oils of this invention, as well as other base oils. This cold test is that prescribed by the Society of Automotive Engineers under the designation, S.A.E. 70R1. The hydraulic fluid under test is maintained at --40 F. for six days. At the end of that time, it should flow in five seconds and show no more than slight opalescence or hazing, and no stratification, or precipitation. The test ratings are based on visual observations, as follows:

( 1 Brilliant (2) Clear (3) Very slight haze, or slight opalescence (3+) Heavy opalescence (4) Slight precipitate through-out (5) Moderate precipitate through-out (6) Heavy precipitate through-out 2 CZHtO, 20% 031150 adduct.

this test. It will be recalled that these unacceptable base oils have pour points which are unduly high.

Brake fluids should not attack and corrode the metals in the brake system. Hydraulic fluids containing the base oils of this invention have acceptable corrosion characteristics. Some typical data on this property are presented in Table III.

TABLE III Corrosion data were obtained on the composition of Example No. 11 by the S.A.E. 70R1 procedure (immersion of metal strips in fluid for 5 days at 210 F.) with addition of- Since small amounts of water may gain access to bydraulic fluid systems through condensation, leakage, or accident, it is essential that hydraulic fluids be miscible with minor percentages of water. In other words, the presence of water in the hydraulic system should not adversely aifect the action of the brakes. The chemical incorporation of mixed oxides into castor oil results in greatly improved water miscibility over that of the unmodified oil. It has been found that, if the water miscibility of a base oil at room temperature is such that clear solutions result upon the incorporation of some 10 weight percent of water into the base oil, the base oils are eminently satisfactory with respect to this property. Base oils of this invention which have a suitable degree of water tolerance include, for example, adducts of castor oil containing a minimum of 30% of mixed oxides. The prior art unmodified oil and esters do not have water miscibilities approaching those of the base oils of this invention, and are quite unsatisfactory in this regard.

From the safety standpoint, it is important that hydraulic fluid base oils have high flash points. The flash points of the base oils of this invention are suitably high.

Because of the presence of rubber parts in brake systems, it is important that the base oils not cause rubber swelling beyond the acceptable maximum limits established by the Society of Automotive Engineers. When natural rubber cups are immersed in the fluid under test for five days at 15 8 F., the size of the cup should not change by more than 0.05 inch. The base oils of this invention have proved to be highly satisfactory in this respect.

In Table IV, the properties of a heavy duty brake fluid containing a base oil of this invention is compared with the heavy duty specification requirements established by the Society of Automotive Engineers. It will be observed that this hydraulic fluid meets the established requirements without difficulty, and especially that the viscosity at -40 F. is far below the established maximum viscosity. This means that this hydraulic fluid can be utilized without difficulty at quite low operating temperatures.

TABLE IV.PERFORMANCE OF HEAVY DUTY BRAKE FLUIDS S.A.E. 70R1 heavy duty specification requirements, base oil a 300 F. (minimum). Bolling point "{boiling point after 6 hrs.

at 295 F., 295 F. (minimum). Flash point Flash 145 F., (minimum). Viscosity (contistokes) {40 F., 1,800 (max.).

130 F., 4.0 (min.). Cold test (5 second flow) 40 F., at 6 days (no ppt. or

strat.). watir toilerance (1 day) (140 F. and 5 sec. flow (no ppt. or strat.).

Neutrality (before and after corro- {Before pH 7 to 11.

sion test). After, pH 6 to 10. Compatibility (140 F. and 40 F.). N 0 ppt. or strat. Evaporation percent 210 F. at 48 hours, 80% (max) Residue test Liquid at 32 F.

Viscosity (centistokes):

40 F., 1,800 max 690 130 F.,4.0rnin 5.5 Cold test second flow 40 F., at 6 da l-2 Water tolerance (1 day) (140 F. and 40 F.) 5 sec flow Pass Neutrality (before and after corrosion test):

Before pH 7 to 11 9. 5 After, pH 6 to 7. 7 Compatibility (140 F. and 40 F.) Pass Evaporation (percent) at 210 F. at 48 hr 80 Residue test Pass Rubber swell (158 F. at 120 hrs.) 036 Corrosion loss (mg/cm. 120 hrs. at 210 15 F Tinned Iron"-.. 02 Steel SAE 100. 01 Alum, SAE 2 02 Cast Iron SAE 111 ()1 Brass SAE 70B 00 Copper SAE 71 00 1 See following table:

Parts by weight Base oil, castor oil Propylene glycol, 40 20 Adduct of 2-butoxyethano1, 80% (021140) 60 And borax, 20% (0311 0) 5 By way of sumarnry, the base oils of this invention completely satisfy the many essential requirements of a satisfactory hydraulic fluid base. As indicated, the instant base oils are characterized by having low yiscosities at reduced temperatures, high viscosity indexes, good water tolerance, and excellent lubricity. In addition, these oils are physically stable and chemically inert to an unusual degree, are miscible with a wide range of oxygen-containing organic diluents, have a negligible effect on rubber, have very low pour points, and are stable at elevated temperatures. As regards the high degree of lubricity of the instant base oils, this is an essential property of oils to be used in hydraulic brake fluids. Moving metal parts invariably form a part of the fluid transmission system, and a low frictional coefiicient is necessary for ease of operation and for minimum abrasion and surface wear. In the lubrication tests 6 prescribed by the Society of Automotive Engineers, the base oils of this invention have been found to be without a peer of all those tested.

What is claimed is:

1. An hydraulic brake fluid consisting essentially of: (a) a base oil which is an adduct of castor oil with a mixture of about 60% ethylene oxide and about 40% propylene oxide with the total mixed oxides being in the range of 25% to 65% by weight of the adduct, said adduct being characterized by having the ability to flow within 5 seconds and being substantially free from haze after being maintained at -40 F. for six days; and (b) an organic oxygen containing alcohol diluent selected from the group consisting of aliphatic monohydric, dihydric, and trihydric alcohols having from 1 to 7 carbon atoms and aliphatic ether alcohols having from 3 to 10 carbon atoms.

2. The fluid of claim 1, in which said diluent is present in an amount of from about 60 to about weight percent, based on the combined weight of said adduct and dliuent.

3. An hydraulic brake fluid consisting essentially of; (a) a base oil which is an adduct of castor oil with a mixture of about 5% to about 50% by weight ethylene oxide, based on the total weight of the adduct, and about 2 /2% to about 50% by weight propylene oxide, based on the total weight of the adduct, said castor oil constituting about 40% to about 60% by weight of the adduct, and (b) a diluent selected from the grou consisting of mono-(lower) alkylene glycols, di-(lower) alkylene glycols, lower alkyl ethers of said glycols, primary mono-hydric (lower) alcohols and secondary mono-hydric-(lower) alcohols.

4. The fluid of claim 3, in which said diluent is present in an amount of from about 60 to about 90 weight percent, based on the combined weight of said adduct and diluent.

5. An hydraulic brake fluid consisting essentially of: (a) a base oil which is an adduct of castor oil with a mixture of about 60% ethylene oxide and about 40% propylene oxide with the total mixed oxides being in the range of 25% to 45% by weight of the adduct, said adduct being characterized by having the ability to flow within 5 seconds and being substantially free from haze after being maintained at 40 F. for six days; and (b) an organic oxygen containing alcohol diluent selected from the group consisting of aliphatic monohydric, dihydric, and trihydric alcohols having from 1 to 7 carbon atoms and aliphatic ether alcohols having from 3 to 10 carbon atoms.

References Cited UNITED STATES PATENTS 2,200,494 5/ 1940 Fife 25279 2,233,382 2/ 1941 De Groote et a1. 260-4106 X 2,451,999 10/1948 Walker 25279 2,469,285 5/ 1959 White 25278 2,588,970 3/1952 Esposito 25279 2,674,619 4/ 1954 Lundsted 260-485 2,755,251 7/1956 Barker 25279 2,758,976 8/1956 Barker 25279 2,944,976 7/ 1960 Waters et a1. 25279 X 2,987,490 6/ 1961 Kirkpatrick et a1. 260410.6 X

FOREIGN PATENTS 764,922 l/1959 Great Britain 25279 876,007 8/1961 Great Britain 25279 853,487 10/1952 Germany 25279 LEON D. ROSDOL, Primary Examiner H. A. PITLICK, Assistant Examiner US. Cl. X.R. 252--76 

